KED CORPUSCLES OF BLOOD. 135 



dent life ; undergoing all their changes whilst floating in the rapidly- 

 circulating current. These Red Corpuscles can scarcely be said to 

 exist in the blood of Invertebrated animals, and their proportion in the 

 blood of Vertebrata varies considerably in the several groups of that 

 sub-kingdom ; they are altogether wanting in the blood of the Amphi 

 oxus or Lancelet, which, although essentially a Fish, has many pecu- 

 liarities that connect it with the lower divisions of the Animal series. 

 They present, in every instance, the form of a flattened disk, which is 

 circular in Man and in most Mammalia (Front. Fig. 1), but which is 

 oval in Birds, Reptiles, and Fishes, and in a few Mammals (Front. Fig. 

 6). This disk is in both instances a flattened cell, whose walls are pel- 

 lucid and colourless, but whose contents are coloured. Like the cor- 

 puscles already described, they may be caused to swell up and burst, 

 by the imbibition of water ; and the perfect transparency and the homo- 

 geneous character of their walls then become evident. (Front. Fig. 8, 

 e.) These Red Corpuscles are not only distinguished from the others 

 by the colour of their contents ; they are also characterized by the ab- 

 sence of the separate molecules, which formed so distinctive a feature 

 in the preceding; and in Oviparous Vertebrata by the presence of a 

 distinct central spot or nucleus, which appears to be composed of an 

 aggregation of minute granules, analogous to those elsewhere diffused 

 through the interior of the cell. The nucleus (where it exists) may be 

 easily obtained separate from the cell-wall and its contents, by treating 

 the red corpuscles, with water. The first effect of this is to render the 

 nucleus rather more distinct, -as is seen by contrasting the corpuscle 

 which has been thus slightly acted on (Front. Fig. 8, a), with the un- 

 altered corpuscle (Front. Fig. 6) of the same animal. After a short 

 time, the corpuscle swells out and becomes more circular (Front. Fig. 

 8, 5); and in a short time longer, the nucleus is seen, not in the centre 

 of the disk, but near its margin (Front. Fig. 8, c, d). Finally, the wall 

 of the cell ruptures ; the nucleus and its other contents are set free ; 

 and whilst the colouring matter is diffused through the surrounding 

 fluid, the cell-walls and the nuclei are separately distinguishable. (Front. 

 Fig. 8, e.) It is remarkable, however, that the Red corpuscles of the 

 blood of Mammals should possess no obvious nucleus ; the dark spot 

 which is seen in their centre (Front. Fig. 1), being merely an effect of 

 refraction, in consequence of the double-concave form of the disk. 

 When the corpuscles are treated with water, so that their form becomes 

 first flat, and then double-convex, the dark spot disappears ; whilst, on 

 the other hand, it is made more evident when the concavity is increased 

 by the partial emptying of the cell, which may- be accomplished by 

 treating the blood-corpuscles with fluids of greater density than their 

 own contents. 



216. The size of the Red Corpuscles is not altogether uniform in the 

 same blood ; thus it varies in that of Man from about the l-4000th to 

 the l-2800th of an inch. But we generally find that there is an ave- 

 rage size, which is pretty constantly maintained among the different 

 individuals of the same species ; that of Man may be stated at about 

 3400th of an inch. The round corpuscles of the Mammalia do not 

 in general depart very widely from this standard ; except in the case of 



